Mushrooms have been grown commercially in the United States and other countries for many years. There are several methods of commercial mushroom cultivation, however, the bed (a.k.a. shelf) and the tray system have been the most popular. In the bed system the receptacles for growing mushroom are stationary. In the tray system, however, the receptacles are portable and can be moved from place to place. Other, less popular, methods of growing mushroom have been the bag system, the ridge bed system and deep trough system.
In the bed system mushrooms are grown in wooden receptacles which are approximately 65" wide.times.60 foot long. These receptacles may be wider or narrower than 65" and/or they can be shorter or longer than 60 feet long. The depth of these receptacles is generally from 6" to 8" deep, however, they can be any suitable size. In what is referred to as a mushroom house these receptacles are usually stacked in four tiers, In each of these tiers six receptacles are usually stacked in a superimposed arrangement so that one mushroom house contains 4 tiers and 24 receptacles.
In the tray system mushrooms are also grown in wooden receptacles. These receptacles or trays can be square or rectangular, however, the most popular size is 48" wide.times.72" long.times.8" deep. In a farm using the tray system approximately 220 of these trays are put into one growing room. The trays are generally stacked four to five trays high and are arranged in eleven rows four stacks to a row. A typical mushroom tray is about 175 cm. long by 120 cm. wide with the tray height being 17.5 cm. and the corner post extending upwardly from the tray sides a further distance of about 12.5-15 cm.
Mushrooms are grown on decaying organic material. This material can be horse manure, hay, cereal straw or a variety of other vegetable wastes. The breakdown of this organic material is accelerated by the mushroom grower by composting. In mushroom growing there are two stages to the composting operation: an outdoor phase generally referred to as Phase I Composting and an indoor phase generally referred to as Phase II Composting. The purpose of composting is to convert the crude, often variable, raw material into a medium rich in nutrition which is specific for the growth of mushrooms.
In the outdoor Phase I Composting the material to be composted is stacked into windrows by a compost turning machine. These windrows can be from 5 ft. to 8 ft. wide and from 5 ft. to 8 ft. high by any length. At this time supplements can be added to the base composting material, for example, chicken manure, and/or protein rich vegetable materials, e.g., cotton seed meal, soya bean meal etc. These supplements have the effect of increasing the microbial populations greatly and also increase the nitrogen content of the final product. Both of these factors are considered important for good yields. After these initial windrows have been formed they may be turned occasionally by the compost turner for the purpose of mixing, watering and aerating the windrow. During this stage the windrow will begin to heat within 24 hours and temperatures as high as 180.degree. F. can be achieved in some parts of the stack. It was learned many years ago that the most productive (in terms of mushroom production) compost is one that is well aerated and held within a specific temperature range during the outdoor composting period e.g. 122.degree. F. to 150.degree. F. It is extremely hard, however, to expose all of the compost to these conditions because of outside atmospheric conditions and because of restricted aeration in various parts of the windrow. FIG. 4 is an example of the zonation that occurs during Phase I. Ideally all of the compost should be exposed to conditions as shown in Zone 2.
After the outdoor composting phase or Phase I, the compost is brought into the growing room by conveyors and filled in the beds or trays that have been previously described. At this time the compost is ready for the indoor composting stage which is commonly called Phase II. The purpose of Phase II is to complete the process which began outdoors in Phase I, however, to do so under controlled conditions so that all of the compost receives the most favorable conditions of Zone 2 of the outside compost windrow. Furthermore, the compost can be uniformly subjected to a period of high temperature which will pasteurize it and ensure that it is free from most mushroom pests and diseases. Because of the construction of the bed or trays is extremely hard to get uniform temperatures during Phase II. Uniformity of the temperature in a mushroom growing bed is crucial, however, due to the construction of the beds this is not possible. The temperature along the sides of the bed (shown in FIG. 6 as "A") is always colder than the temperature in the center of the bed (shown as "B"). This is a disadvantage when bringing the compost up to temperature because when the center of the bed has reached the optimum temperature the sides are still cold. Also when bringing the bed temperature down from, for example, 140.degree. to 80.degree. F., in preparation for spawning when the sides have reached the optimum of 80.degree. F., the center of the bed is still too hot to plant the spawn. For these reasons the mushroom farmer has to constantly make compromises during Phase II as well as the rest of the growing cycle. If these temperature differentials could be overcome, the growing cycle could be shortened and the amount of mushrooms grown in one crop could be increased which would greatly increase the profitability of a farm. There would also be a substantial savings in heating and cooling energy if the above mentioned temperature differentials could be overcome.
The complete Phase II process takes approximately 10 days. At the end of this ten day process the bed temperatures are brought down to approximately 58.degree. F. and prepared for the next operation which is spawning. The mushroom beds (or trays) are then spawned (which is similar to the planting of seed in conventional farming) and supplemented. The next 14 days are commonly referred to as "spawn run". During this time frame the temperatures begin to rise because of the biological activity of the spawn and air conditioning must be used to hold the temperature at the level of 58.degree. F. The same temperature zonation that was experienced during Phase II composting occurs during the spawn run stage and throughout the growing cycle.
After approximately 14 days the mushroom spawn has completely overtaken the compost and at this time a casing layer of peat moss or other suitable material is applied to the top of the compost.
Mushrooms will not occur in great numbers unless this casing layer is applied to the bed of compost. Approximately 18 to 22 days after casing mushroom appear and may be harvested.